The present invention relates to an improved friction member for restraining sliding movement of a sliding ring such as a lens hood ring or a zooming ring in a photographing lens.
Heretofore, a sliding friction member made of woolen cloth or the like has been bonded to the inner wall of the sliding part of such a sliding ring to fix the sliding ring, to absorb shocks which may occur during sliding, and to prevent play in the sliding ring. The woolen cloth must be glued to the inner wall of a lens hood ring or the like, which is difficult to do in production. Also, the use of woolen cloth results in a relatively high material cost. In addition, such a woolen cloth member has a rather low wear resistance.
An improved sliding friction member of this type is disclosed in Japanese Utility Model Application Publication No. 16347/1978. In accordance with the technique therein disclosed, to restrain movement of the hood ring or the like, instead of woolen cloth, a plastic material is employed, with a metal member fitted to a sleeve-shaped plastic member. More particularly, a piano wire or the like is inserted into a sleeve of an elastic material having a high wear resistance, such as nylon, vinyl or Teflon (TM), and is formed into a polygonal ring having regularly arranged long and short sides. The ring thus formed is fitted into the receiving groove of the sliding part of the lens hood ring or the like while being urged radially inwardly. Since the elastic member is elastically urged inwardly, the long sides abut the outer wall of the inner cylinder, while the short sides are elastically urged to expand outwardly. As a result, the polygonal spring member abuts against the receiving groove cut in the inner wall of the inner cylinder, thereby maintaining the outer cylinder stable. The object is to provide a click stop function by utilizing a step or the like of the inner cylinder to restrain movement of the lens hood ring or the like.
However, this approach is disadvantageous in that, since the metal wire is inserted into the sleeve-shaped plastic material and it is formed into the polygonal ring having long and short sides regularly arranged as described above, the manufacture of the component is relatively difficult and high in cost.
In addition, as the elastic member presses against the outer wall of the inner cylinder, the painted outer wall of the inner cylinder may be scratched. This is another drawback of the conventional sliding friction member.
Accordingly, objects of the invention are to provide a sliding friction member for a lens sliding ring which will not scratch the coated surface of the sliding part and which allows a smooth sliding operation with suitable sliding friction and with proper depression force.